We have been studying the structure and function of the two ferritins in rat heart for some years. Our present objectives are: (a) to complete structural work on ferritins from rat and human heart, with emphasis on size and shape characteristics, and the contributions of post-translational modification (including carbohydrate addition and gamma-carboxylation) and gene expression to subunit composition and properties; using sedimentation, 2-dimensional techniques for subunit separation, etc; (b) to embark on extensive studies of the mechanism of iron uptake, distribution and metabolism in rat heart and the role of both ferritins in the process, using 59Fe and various separation techniques; focusing especially on the possibilities that: (1) heart contains iron receptors, transfer proteins, and/or a pool of non-protein bound iron, as yet unidentified, which play a role in cardiac iron metabolism, and (2) that this is altered in infancy and iron deficiency; (c) to pursue possibilities that cardiac ferritins are released preferentially over other proteins during myocardial cell damage (using heart perfusion), and that these ferritins are linked to the metabolism of vitamin K. These objectives spring from many observations, including our more recent findings that: (1) heart ferritins are peculiar in structure vs. other ferritins; (2) they may contain gamma-COOH glutamate residues (implicating vitamin K): (3) both are probably present in myocardial cells, and during cell isolation are lost preferentially over other proteins; (4) during infancy and iron deficiency much larger amounts of ferritin accumulate in heart, in response to injection of excess iron, than is the case for normal animals. It is expected these studies will be significant for our understanding of the role of iron and ferritin in heart cell function, the relation between cell damage and ferritin release, and the contributions of gene expression and post-translational modification to ferritin structure.